Ammonia is a common, naturally occurring compound in the environment.It can be naturally broken down into one atom of nitrogen and three atoms of hydrogen, its chemical formula therefore being NH3. Ammonia is a key intermediary in the nitrogen cycle for plants and animals, given that the atmosphere consists of nearly 80% nitrogen. It is essential for many biological processes.

In fact, ammonia is among the most abundant gasses in the environment. Used as a refrigerant, the colourless gas carries the designation R717 / R-717. Given its abundance in nature, ammonia is referred to as a “natural refrigerant”.

Traditionally, refrigerant-grade ammonia has been used as a 99.98% pure substance, free of water and other impurities. It is readily available, inexpensive, and capable of absorbing large amounts of heat when it evaporates.Lately, new blends incorporating ammonia have been shown to provide additional benefits in terms of lower discharge outlet temperature, a lower compression ratio, and a higher refrigeration capacity. Blends include the hydrocarbons propane (R290), octafluoropropane (R218), octafluorocyclobutane (RC318), or isobutane (R600a). The blend R723 - consisting of 60% ammonia and 40% dimethyl ether - promises further potential in high temperature heat pumps.

Yes, with proper handling. In any mechanical refrigeration system, leaks will occur. This fact is exacerbated when the leaks involve odourless refrigerants hazardous to human health, or otherwise harmful for the environment.

Having been used as a refrigerant for more than 150 years, ammonia has a long safety record. The inherent safety of ammonia comes from its characteristic odour, which signals even the smallest leak, at concentrations far lower than any dangerous level. Moreover, its density and very limited range of flammability, advances in safety mechanisms and system designs (plate heat exchangers, separate sealed compartments, leak detection systems, electrical switching outside the compartments etc.), well-trained individuals working with R717 systems, as well as industry codes and standards have made sure that ammonia poses hardly any risk to human health.

As an example, the United States Chemical Safety Board (CSB) reports that R717 incidents led to only four fatalities in the ten-year period from 1994 to 2004. This compares with over 800 deaths from lightning strikes in the USA during the same period.

Ammonia is difficult to ignite and exhibits a narrow range of flammability. It is flammable only at high concentrations and under extremely limited conditions. Because ammonia will not sustain a flame on its own, ignition of ammonia vapour requires an uninterrupted external flame source. Ammonia’s burning velocity, at a maximum of 8cm/s, is substantially lower than other flammable refrigerants, and is not high enough to create an explosion. Properly designed ammonia refrigeration systems that are well ventilated and free of open flames or ignition sources are safe against potential explosion.

Yes. Ammonia carries a B2 safety classification, meaning that it can be toxic for humans at high concentrations. However, as even the slightest traces of ammonia can be detected in the air, a safe and immediate repair of a system leak is possible. Moreover, the easily detectable and penetrating odour will encourage individuals to leave the immediate area of release before any harmful concentration will occur. The safety record of ammonia refrigeration is also due to the fact that ammonia is 1.7 times lighter than air and thus easily vented by mechanical means into the atmosphere. If a leak occurs in a refrigeration system under pressure, only the pressurized gas and, absent additional heat, a smaller amount of the liquid in that space will be released.

The facts: The human body can handle ammonia in small quantities. Any amount in the atmosphere below 20 parts per million (ppm) is regarded as not dangerous. Already at amounts of up to 53 ppm, ammonia’s characteristic odour will be noticeable. At amounts of 300-400ppm, prolonged exposure will become unpleasant, and only in amounts over 700ppm it can start affecting human health. As a result, the incidence of fatality and serious injury in R717 systems is extremely low.

No. Ammonia has a Global Warming Potential (GWP) of 0, meaning it doesn’t add to the greenhouse effect linked to global warming. In fact, ammonia, one of the most common compounds found in nature, is essential to the earth’s nitrogen cycle and its release in the atmosphere is immediately recycled. The use of ammonia as a refrigerant is therefore consistent with international agreements on reducing global warming and ozone depletion.

To assess the complete environmental performance of refrigerants and their systems, both Direct and Indirect Emissions have to be considered:

Firstly, using ammonia reduces the Direct greenhouse gas (GHG) emissions. This is due to its Global Warming Potential (GWP) of 0, compared to a GWP of 1,700 for R22 and 3,260 for R404a, and even higher values for other chemical refrigerants. Why is this important? As an example, from a typical industrial refrigeration system 10-25% of the total refrigerant charge is emitted to the atmosphere every year. Assuming that leakage rates are the same, ammonia will thus spare the planet tonnes of greenhouse gases compared to any other chemical refrigerant currently used. In addition, leakage rates for ammonia are considerably lower than for any other refrigerant as the gas is detected much earlier due to its characteristic odour.

Secondly, ammonia also leads to lower Indirect GHG emissions by maximising energy efficiency of equipments in which they are used. This is due to a combination of factors, including its favourable thermodynamic characteristics. As a result, ammonia systems use less primary energy to produce a certain refrigeration effect compared to other commonly used refrigerants. Its indirect global warming effect is therefore one of the lowest of all refrigerants.

Presently, there are an estimated two billion metric tons of ammonia present in the world. Of this amount, approximately five percent is man-made. Approximately 18 million metric tons of ammonia are produced annually in North America alone, and of this amount, less than two percent is used for refrigeration.

No. Ammonia was first used as a refrigerant in the 1850s in France and was applied in the United States in the 1860s for artificial ice production. The first patents for ammonia refrigeration machines were filed in the 1870s. From all the refrigerants used in food processing, ice rinks, chillers and other applications, only ammonia has secured a lasting role as a refrigerant. Even when halocarbons became the refrigerants of choice, ammonia remained the most used refrigerant for industrial applications in many countries. Because of ammonia’s proven applicability as a safe and efficient refrigerant for over 150 years, it is immediately available for wider usage and new applications. Today, ammonia remains the most commonly used refrigerant in large systems to process and preserve food and beverages.

Ammonia is capable of absorbing large amounts of heat when it evaporates. For industrial refrigeration, ammonia is generally accepted as the most efficient and cost effective refrigerant available. This, in turn, brings important benefits to consumers, as the lower operating costs contribute to lower food prices.

For chillers, ammonia can also offer optimal performance. As an example, the central ammonia chilling plant of London Heathrow’s new Terminal 5 uses four chillers, each with a cooling capacity of 6.6 mW, or 1,875 tonnes. The large-scale R717 chillers reduce energy consumption by at least 30% compared to smaller local chillers. Moreover, storing the chilled water reduces the system capacity and takes advantage of night electricity rates.

Food processing, Cold storage & Delivery: Ammonia refrigeration is the backbone of the food industry for freezing and storage of both frozen and unfrozen foods in many parts of the world (including fruits, vegetables, meat, poultry, fish, dairy, ice cream, beverages). In the range 50 kW to 200 kW ammonia may be used, and for larger freezers ammonia is almost always preferred due to improved energy efficiency and reduced leakage.

Petrochemical & Pharmaceutical industry, Mining: For many years, ammonia has been the refrigerant of choice in large industrial refrigeration applications, including process cooling, cold storage, the production of ice for use in chemical reactions, and mining. Ice plants are typically far larger than those found in the food industry.

Air Conditioning: Ammonia is increasingly used for air conditioning in public buildings, hospitals, colleges and office parks, as well as to enhance the efficiency of power generation facilities. Ammonia refrigeration has also been used to provide air conditioning for the International Space Station and the theme park Biosphere II, in the USA.

Chillers: Chillers using R717 and a secondary heat transfer fluid (intrinsic to chillers) are available in the capacity range from 200 to 2000 kW with a few larger models. They allow for the safe use of ammonia in large buildings. Ammonia can be used in absorption chillers – with water as the absorbent –, in screw chillers, or in reciprocating chillers. The new Terminal 5 of Heathrow, one of the world’s largest airports, is using a central ammonia chilling plant to provide all heating and cooling.

Supermarkets: More recently, ammonia has been used in conjunction with a secondary refrigerant such as carbon dioxide in a ‘cascade’ system, meaning that less ammonia is required to achieve satisfactory results, and that the ammonia charge can be contained in a plant room or other safe environment.

Marine refrigeration / Fishing vessels: R717 has been increasingly used in marine refrigeration equipment. Applications include its use for reefer ships, as proposed refrigerant for sorption ice machines, and for fishing vessels both as single refrigerant as well as in combination with CO2 (R744), especially for low temperature uses.

Heat pumps: Absorption heat pumps for hot water space heating are mostly gas-fired and commonly provide cooling simultaneously with heating. An updated family of absorption machines is available using an ammonia-water cycle powered by natural gas. R717 has also been used in medium-size and large capacity heat pumps. In addition, progress has been made in the field of using ammonia for residential heat pumps, with initial prototypes with an output of 6 kW having reportedly worked reliably with ammonia charges of less than 100g.

Leisure industry, Ice Rinks, Ski Slopes: Ammonia can be used for refrigeration purposes in ice rinks and ski Slopes, and in parallel, for the heating of leisure facility premises.. Europe’s largest open air stadium with an ice rink (Karlstad, Sweden), and the world’s third largest indoor snow park (Dubai, Emirates) are both using R717 to constantly produce ice and snow.

Large ammonia refrigeration systems contain up to 60,000 kg of refrigerant. Installations for food processing and industrial plant refrigeration typically range from 5 to 100 tonnes. Around the world large R717 systems are subject to increasingly stringent safety regulations and pressure is being placed on companies to reduce the size of ammonia refrigerant charges. Therefore, owners of large industrial plants are starting to use ammonia in conjunction with a secondary refrigerant such as carbon dioxide (R744) or potassium acetate, meaning that an up to 90% reduced ammonia charge is needed compared to an ammonia-only system. The reduction of charge does not lead to any performance compromises.

Ammonia is compatible with many, but not all materials suited to synthetic refrigerants. As an example, it is only compatible with some commonly used refrigeration system lubricants, excluding polyol ester (POE) and poly vinyl ether (PVE) lubricants, and it has only limited applications with poly alkylene glycol (PAG) lubricants. To accommodate for the safety requirements in an R717 system, some modifications to an existing system design might be needed to integrate safety features and ensure compatibility. Ammonia is not compatible with most types of electrical wiring insulation. Metals of construction inside ammonia systems normally are limited to carbon and stainless steel, but good compatibility of ammonia with copper and copper alloys in systems with careful moisture control have been reported, provided that there is no presence of water leading to copper corrosion. Aluminium is compatible with ammonia, but it is sensitive to corrosion in water circuits due to the presence of chlorides.

The use of ammonia is subject to a wide range of technical and safety standards in different world regions, which, when thoroughly followed, ensure the refrigerant’s safe and highly efficient use. Workers handling ammonia installations must be knowledgeable of emergency procedures and applicable standards. In addition, regulations require regular inspection of safety equipment and ongoing training to prepare workers in the event of an emergency, which, compared to other risks in society, are extraordinarily rare. While industry-driven codes and standards include certain system engineering and design standards and operating codes, federal regulations prescribe workplace safety rules when using ammonia, environmental requirements (including reporting and risk management obligations), and transportation rules. These requirements create regulatory burdens for ammonia refrigeration applications, as facilities have to follow Process Safety Management (PSM) and Risk Management (RMP) Programs linked to paperwork and document retention.

Ammonia systems designed during the past 20-30 years in accordance with pressure vessel legislation and limitations on the amount of ammonia used, are very high quality with excellent standards of safety. For older systems, effective training of personnel with operational responsibilities is worthwile as the most effective low-cost preventive measure.

Industrial Refrigeration: Today, ammonia remains the most cost-effective and energy-efficient option for all types of industrial equipment. In fact, R717 makes up 15% of the total refrigerant market. R717 is expected to remain the preferred choice for large installations once ozone-depleting substances will be ruled out under international agreements. In the US and Canada ammonia is well regulated and enjoys a wide-spread use. In Europe, R717 has been widely adopted for industrial refrigeration in the UK and Germany but is more tightly regulated in France, Belgium, the Netherlands and Italy, and it is consequently less common. It is the most common alternative to HFCs for larger systems in Scandinavia, mainly as a result of restrictions and taxation on greenhouse gases. First installations in Australia have proved the efficiency of R717 plants. As a most recent example, ammonia freezes 6000 head of lamb every day in one of Australia’s largest meat processing companies, being capable of freezing 1610 bulk packed export meat cartons with a 24-hour turn around.

Commercial Refrigeration: The use of ammonia in cascade supermarket refrigeration systems is growing, especially in countries with stringent limitations on the use of HCFCs and HFCs, such as Scandinavia.

Chillers: Although the use of R717 is still limited, this market is expected to grow. As a most recent example, a central ammonia chilling plant provides continuous supply of hot and chilled water for heating and air conditioning to Terminal 5 of London’s airport Heathrow.

Heat pumps: R717 has been applied in medium-size and large capacity heat pumps, mainly in Scandinavia, Germany, Switzerland, and the Netherlands.

From a purely economic analysis, ammonia should find broader applications as a refrigerant than it currently enjoys. However, to realise ammonia’s full potential as a refrigerant, safety regulations and technical standards around the world will be required to become more tailored to ammonia refrigeration systems, and consistent across world markets. Regulatory restrictions and a lack of clear encouragement from policy makers to move towards natural refrigerants currently impede a wider spread of R717. To sum up, a deficit of promotion, a lack of technical and regulatory harmonisation, missing guidance for operators, and a patchwork of national safety regulations pose excessive administrative and financial burden on the ammonia business. Politicians’ recognition of ammonia as a sustainable alternative to ozone-depleting and high global warming substances under international environmental programs could lift these barriers. To achieve this goal, data on the performance and use of R717 has to be updated and spread in coverage to allow for an informed choice.